Animals,
vegetables and micro- organisms
comprise of an ecosystem.
The fungi act like decomposers
when unfolding rubbish in
inorganic compounds. This
way they close the cycle
of the matter.

Towards 1950 the
ecologists elaborated the scientific
notion of ecosystem, defining it as
the unit of study of ecology. In agreement
with such definition, the ecosystem
is a delimited space unit, integrated
on the one hand, by the alive organisms
and the environment in which these
are developed, and by another one,
the interactions of the organisms
to each other and with their surroundings.
In other words, the ecosystem is a
unit formed by biotic factors (or
alive members like vegetables and
the animals) and abiotic factors (components
that lack life, like for example minerals
and water), in which vital interactions
exist, energy flows and the matter
circulates.

An example of ecosystem
in that the elements included in the
definition can be seen clearly is
the tropical forest. There thousands
of vegetal and animal species, inhabit
the air and the ground; in addition,
million interactions between the organisms,
and these take place and also with
their surrounding. The extension of
an ecosystem is always relative: it
doesn't constitute an indivisible
functional unit, but that it is possible
to subdivide it in infinity of units
of so large minor. For example, the
ecosystem forest includes, as well,
other more specific ecosystems like
the one than constitute the glasses
of the trees or a fallen trunk.

The habitat and
the ecological niche

Two concepts in
relation with the one of ecosystem
are the one of habitat and the one
of ecological niche. The habitat is
the physical place of an ecosystem
that bring together the natural conditions
where a species lives and to which
it is adapted. The ecological niche
is the way in which an organism is
related to the biotic and abiotic
factors of its environment. It includes
the physical training conditions,
chemical and biological that species
needs to live and to reproduce in
an ecosystem. The temperature, the
humidity and the light are some of
the physical and chemical factors
that determine the niche of species.
Between the biological conditioners
they are the type of feeding, the
predators, the competitors and the
diseases, that is to say, species
that compete by the same conditions.

A dynamic unit

The ecosystem experiences
constants modifications that sometimes
are temporary and other cyclical ones
(they are repeated in the time).

The biotic elements
can react before a change of the physical
conditions of environment; for example,
the deforestation of a forest or a
fire has direct consequences on the
fertility of the ground and affects
the food web too.

In an aquatic
ecosystem the biodiversity, or
the number of vegetal and animals
species that live in him, is minor
than in a terrestrial one. The
nutritious base is in the phytoplankton
and zooplankton.
The scale goes in ascent from
the fish and batrachians to the
aquatic birds like the duck, and
aerial like the eagle.

The ecological
succession

The ecological succession
is the replacement of some elements
of the ecosystem by others in the
course of the time. Thus, a certain
area is colonized by more and more
complex vegetal species. If the environment
allow it, the appearance of mosses
and lichens is happened by grass,
soon by shrubs and finally by trees.
The state of balance reached once
the evolution has been completed,
denominates climax. In him, the modifications
occur between the members of same
species: for example, new trees replace
the old ones.

There are two types
of successions: primary and secondary.
First it happens when start from a
land in where never there was life.
This type of process can last thousands
of years. The secondary succession
is the one that is registered after
a disturbance, for example, a fire.
In this case the environment contains
organic nutrients and remainders that
facilitate the growth of vegetables

In
a trofic pyramid the nourishing
structure of an ecosystem is appraised
in where they coexist producing,
consuming and decomposers. The
vegetables elaborate organic matter
through the photosynthesis. The
herbivorous are fed on them, and
they are eaten as well by carnivorous
pregivers or. When these organisms
are dying, their rest are transformed
into assimilable substances by
it plants, process in which takes
part the decomposers organisms.

PREDATORS

CARNÍVORES

HERBIVOROUS

PRODUCERS

DECOMPOSERS

The food web

In the operation
of the ecosystems it doesn't happen
waste some: all the organisms, died
or alive, are potential food source
for other beings. An insect feeds
itself on a leaf; a bird eats the
insect and simultaneously is devoured
by a zoo bird.

When dying these
organisms are consumed by the decomposers
that will transform them into inorganic
substances. These relations between
the different individuals from an
ecosystem constitute the food web.

The producers are
the alive organisms that make their
own organic food, that is to say,
the green vegetables with chlorophyll,
that make photosynthesis. By means
of this process, the mineral substances
are transformed in organic, compounds
usable by all the alive forms. Other
producers, like certain bacteria,
elaborate their organic compounds
from inorganic substances that find
in the outside, with no need of solar
light.

The consumers, are
organisms that cannot synthesize organic
compounds, and for that reason they
are fed on other alive beings. According
to the nutrients that use and the
place that occupy within the food
web, the consumers classify themselves
in four groups: primary or herbivorous,
secondary or carnivorous, tertiary
or super carnivorous and decomposers.

The herbivorous
are fed directly on vegetables. The
secondary or carnivorous consumers
take advantage of the organic matter
produced by their prey. Between the
tertiary or super carnivorous consumers
are the scavenging animals, that feed
themselves on corpses.

The decomposers
are the bacteria and fungi in charge
to consume the last organic rest of
producers and dead consumers. Its
function is essential, because they
turn the dead matter into simple inorganic
molecules. That material will be absorbed
again by the producers, and recycled
in the production of organic matter.
In this way it is renewed the cycle
of the matter, closely tie with the
energy flow.

This organization
of the ecosystems is valid as much
for terrestrial environment as for
the aquatic ones. In both are producers
and consumers. Nevertheless, the terrestrial
ecosystems have greater biological
diversity than the aquatic ones. Indeed
by that biological wealth, and its
greater variability, the terrestrial
ecosystems offer more ecological amount
of different habitats and more niches.